The present invention relates to an apparatus and a microchip for sorting micro particles. More specifically, the present invention relates to a micro-particle sorting apparatus and the like, that detects properties of micro particles, which flow through a flow path formed in a microchip, within the chip, discharges liquid drops containing the micro particles to the outside of the chip, and controls the movement directions of the liquid drops on the basis of the detected properties of the micro particles for sorting.
Conventionally, in order to identify properties of micro particles such as biologically-relevant micro particles such as cells, microorganisms, liposomes or synthetic particles such as latex particles, gel particles, or industrial particles, there has been utilized an apparatus that introduces dispersion liquid of the micro particles into the flow path, and optically measures the properties of the micro particles that have been introduced into the flow path.
In particular, regarding the biologically-relevant micro particles, there has been widely used an apparatus called a flow cytometry (flow cytometer) (see Non-Patent Document 1). As flow cytometries, there are those that are designed only for measurement of the properties of the micro particles, or those that are configured to be capable of sorting only the micro particles each having a predetermined property on the basis of the measurement result. Regarding the latter, particularly an apparatus for a cell being as a sorting target is called “cell sorter.” The cell sorter currently available in the market is capable of measuring and sorting properties of cells at high speed, for example, several thousands to several tens thousands of cells per second.
In the conventional flow cytometry, properties of the size, the structure, and the like of the micro particles such as cells or micro beads are measured in the following manner. First, in a flow cell, sample solution containing micro particles being as measurement target is caused to flow into the center of a laminar flow of sheath liquid, to thereby arrange the micro particles in line in the flow cell. Next, in an optical detection portion, the micro particles arranged and flowing in the flow cell are irradiated with measurement light, and scattering light or fluorescence generating from the micro particles is detected. In this manner, the properties of the micro particles are measured. Subsequently, in a case where the sorting of the micro particles is performed, the sample liquid is discharged into a space outside the flow cell as liquid drops containing the micro particles, and movement directions of the liquid drops are controlled, to thereby sort the micro particles each containing a predetermined property.
Patent Document 1 (FIG. 7) discloses an apparatus, as the conventional cell sorter, which includes a fluid system for arranging cells stained with fluorescent labeling reagent or the like in line in the flow cell, and a sorting system for controlling the movement directions of the liquid drops discharged into the space outside the flow cell.
Each of those conventional flow cytometries (cell sorters) cannot be easily disposed of by a user because the flow cell part constituting the flow path system is made of expensive quartz and is constituted of the orifice part separate from the flow cell. Thus, even if the flow cell part and the orifice part are sufficiently washed in every measurement, there is a fear that cross contamination of samples between measurements occur. Further, the space constituting the sorting system is set as an open space or a space having low air tightness, and hence contamination materials such as micro liquid drops (aerosol) generating during formation of the liquid drops may be mixed into a sample at the time of measurement, or biohazard such as infection or exposure with respect to apparatus users due to the aerosol may occur. The cross contamination between the samples, the contamination of the sample, the biohazard with respect to the users, and the use of the flow cell and the orifice part, which are expensive, as described above remain obstacles particularly in a case of using stem cells or the like, which have been sorted by the cell sorter, for regenerative medicine.
As a technique for addressing the cross contamination between the samples, the contamination of the sample, the biohazard with respect to the users, and the use of the flow cell and the orifice part, which are expensive, there has been, in recent years, developed a microchip including a silicon or glass substrate on which an area for performing a chemical and biological analysis and a flow path are provided. The analysis system using such a microchip is called μ-TAS (micro-total-analysis system), lab-on-a-chip, biochip, or the like.
As an example of applying the μ-TAS to the micro-particle sorting technique, there is a micro-particle sorting technique of optically, electrically, or magnetically analyzing the properties of the micro particles in the flow path or the area provided on the microchip. For example, Patent Document 2 discloses a micro-particle classifying microchip including, on a substrate, a micro-particle-containing solution introducing flow path, a sheath flow forming flow path arranged in at least one side portion of that flow path, a micro-particle measuring location for measuring the introduced micro particles, and two or more micro-particle classifying flow paths for classifying and collecting the micro particles, which are placed downstream with respect to the micro-particle measuring location. This microchip includes electrodes near the opening of the flow path from the micro-particle measuring location to the micro-particle classifying flow paths. According to the micro-particle sorting apparatus including this microchip, it is possible to control the movement directions of the micro particles due to interaction with respect to the electric field of the electrodes, to thereby sort the micro particles.
In the flow cytometry (cell sorter) applying the μ-TAS, the microchip enabling a disposable use (which is disposable) can constitute the flow path system. Therefore, the cross contamination of the samples between measurements does not occur. Further, the sorting system can be arranged in the airtight flow path provided in the chip. Therefore, no contamination material such as the aerosol is mixed into the sample during measurement. However, it is necessary to deliver at high pressure the liquid containing the micro particles through the flow path provided in the chip. Further, it is necessary to perform the control of the movement directions of the micro particles in such a state that the micro particles are flowing in the liquid. Therefore, it is difficult to increase the flowing velocity of the micro particles and the sorting speed, and to measure and sort the properties of the cells at high speed, for example, several thousands to several tens thousands of cells per second as in the conventional flow cytometry (cell sorter).